Development of a windowless multi-wire proportional chamber (MWPC) counting system for measuring extended-area beta source

A windowless MWPC counting system has been developed to measure surface emission rate of extended-area sources. A new anode and guard plane design gives better electric-field uniformity in the (250×200) mm2 sensitive volume relative to a previous-generation MWPC at KRISS, which has been used as a national standard with uncertainty <1%. The conditions of stable operation for the new MWPC system were studied, and the uncertainty was estimated with an extended-area 36Cl source. The relative combined standard uncertainty was evaluated to be 0.23%, a 50% improvement over the previous-generation MWPC counting system.